# Copyright 2015 The TensorFlow Authors. All Rights Reserved.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
# ==============================================================================
"""## Functions for copying elements from one graph to another.

These functions allow for recursive copying of elements (ops and variables)
from one graph to another. The copied elements are initialized inside a
user-specified scope in the other graph. There are separate functions to
copy ops and variables.
There is also a function to retrive the copied version of an op from the
first graph inside a scope in the second graph. 

@@copy_op_to_graph
@@copy_variable_to_graph
@@get_copied_op
"""

from __future__ import absolute_import
from __future__ import division
from __future__ import print_function

from copy import deepcopy
from tensorflow.python.ops.variables import Variable
from tensorflow.python.client.session import Session
from tensorflow.python.framework import ops

__all__ = ["copy_op_to_graph", "copy_variable_to_graph", "get_copied_op"]


def copy_variable_to_graph(org_instance, to_graph, scope=""):
    """Given a `Variable` instance from one `Graph`, initializes and returns
    a copy of it from another `Graph`, under the specified scope
    (default `""`).

    Args:
    org_instance: A `Variable` from some `Graph`.
    to_graph: The `Graph` to copy the `Variable` to.
    scope: A scope for the new `Variable` (default `""`).

    Returns:
        The copied `Variable` from `to_graph`.

    Raises:
        TypeError: If `org_instance` is not a `Variable`.
    """

    if not isinstance(org_instance, Variable):
        raise TypeError(str(org_instance) + " is not a Variable")

    #The name of the new variable
    if scope != "":
        new_name = (scope + '/' +
                    org_instance.name[:org_instance.name.index(':')])
    else:
        new_name = org_instance.name[:org_instance.name.index(':')]

    #Get the collections that the new instance needs to be added to.
    #The new collections will also be a part of the given scope,
    #except the special ones required for variable initialization and
    #training.
    collections = []
    for name, collection in org_instance.graph._collections.items():
        if org_instance in collection:
            if (name == ops.GraphKeys.VARIABLES or
                name == ops.GraphKeys.TRAINABLE_VARIABLES or
                scope == ''):
                collections.append(name)
            else:
                collections.append(scope + '/' + name)

    #See if its trainable.
    trainable = (org_instance in org_instance.graph.get_collection(
        ops.GraphKeys.TRAINABLE_VARIABLES))
    #Get the initial value
    with org_instance.graph.as_default():
        temp_session = Session()
        init_value = temp_session.run(org_instance.initialized_value())

    #Initialize the new variable
    with to_graph.as_default():
        new_var = Variable(init_value,
                           trainable,
                           name=new_name,
                           collections=collections,
                           validate_shape=False)

    return new_var


def copy_op_to_graph(org_instance, to_graph, variables,
                     scope=""):
    """Given an `Operation` 'org_instance` from one `Graph`,
    initializes and returns a copy of it from another `Graph`,
    under the specified scope (default `""`).

    The copying is done recursively, so any `Operation` whose output
    is required to evaluate the `org_instance`, is also copied (unless
    already done).

    Since `Variable` instances are copied separately, those required
    to evaluate `org_instance` must be provided as input.

    Args:
    org_instance: An `Operation` from some `Graph`. Could be a
        `Placeholder` as well.
    to_graph: The `Graph` to copy `org_instance` to.
    variables: An iterable of `Variable` instances to copy `org_instance` to.
    scope: A scope for the new `Variable` (default `""`).

    Returns:
        The copied `Operation` from `to_graph`.

    Raises:
        TypeError: If `org_instance` is not an `Operation` or `Tensor`.
    """

    #The name of the new instance
    if scope != '':
        new_name = scope + '/' + org_instance.name
    else:
        new_name = org_instance.name

    #Extract names of variables
    copied_variables = dict((x.name, x) for x in variables)
 
    #If a variable by the new name already exists, return the
    #correspondng tensor that will act as an input
    if new_name in copied_variables:
        return to_graph.get_tensor_by_name(
            copied_variables[new_name].name)

    #If an instance of the same name exists, return appropriately
    try:
        already_present = to_graph.as_graph_element(new_name,
                                                    allow_tensor=True,
                                                    allow_operation=True)
        return already_present
    except:
        pass

    #Get the collections that the new instance needs to be added to.
    #The new collections will also be a part of the given scope.
    collections = []
    for name, collection in org_instance.graph._collections.items():
        if org_instance in collection:
            if scope == '':
                collections.append(name)
            else:
                collections.append(scope + '/' + name)

    #Take action based on the class of the instance

    if isinstance(org_instance, ops.Tensor):
 
        #If its a Tensor, it is one of the outputs of the underlying
        #op. Therefore, copy the op itself and return the appropriate
        #output.
        op = org_instance.op
        new_op = copy_op_to_graph(op, to_graph, variables, scope)
        output_index = op.outputs.index(org_instance)
        new_tensor = new_op.outputs[output_index]
        #Add to collections if any
        for collection in collections:
            to_graph.add_to_collection(collection, new_tensor)
 
        return new_tensor

    elif isinstance(org_instance, ops.Operation):

        op = org_instance

        #If it has an original_op parameter, copy it
        if op._original_op is not None:
            new_original_op = copy_op_to_graph(op._original_op, to_graph,
                                            variables, scope)
        else:
            new_original_op = None

        #If it has control inputs, call this function recursively on each.
        new_control_inputs = [copy_op_to_graph(x, to_graph, variables,
                                            scope)
                              for x in op.control_inputs]

        #If it has inputs, call this function recursively on each.
        new_inputs = [copy_op_to_graph(x, to_graph, variables,
                                    scope)
                      for x in op.inputs]

        #Make a new node_def based on that of the original.
        #An instance of tensorflow.core.framework.graph_pb2.NodeDef, it
        #stores String-based info such as name, device and type of the op.
        #Unique to every Operation instance.
        new_node_def = deepcopy(op._node_def)
        #Change the name
        new_node_def.name = new_name

        #Copy the other inputs needed for initialization
        output_types = op._output_types[:]
        input_types = op._input_types[:]

        #Make a copy of the op_def too.
        #Its unique to every _type_ of Operation.
        op_def = deepcopy(op._op_def)

        #Initialize a new Operation instance
        new_op = ops.Operation(new_node_def,
                               to_graph,
                               new_inputs,
                               output_types,
                               new_control_inputs,
                               input_types,
                               new_original_op,
                               op_def)
        #Use Graph's hidden methods to add the op
        to_graph._add_op(new_op)
        to_graph._record_op_seen_by_control_dependencies(new_op)
        for device_function in reversed(to_graph._device_function_stack):
            new_op._set_device(device_function(new_op))

        return new_op

    else:
        raise TypeError("Could not copy instance: " + str(org_instance))


def get_copied_op(org_instance, graph, scope=""):
    """Given an `Operation` instance from some `Graph`, returns
    its namesake from `graph`, under the specified scope
    (default `""`).

    If a copy of `org_instance` is present in `graph` under the given
    `scope`, it will be returned.

    Args:
    org_instance: An `Operation` from some `Graph`.
    graph: The `Graph` to be searched for a copr of `org_instance`.
    scope: The scope `org_instance` is present in.

    Returns:
        The `Operation` copy from `graph`.
    """

    #The name of the copied instance
    if scope != '':
        new_name = scope + '/' + org_instance.name
    else:
        new_name = org_instance.name

    return graph.as_graph_element(new_name, allow_tensor=True,
                                  allow_operation=True)
